While the digital carriers are primarily in the 100-200 kHz (offset from the carrier) range, there can be some interference if you're using SCAs of 67 kHz or higher AND additional HD channels. The additional HD channels start encroaching on the lower end of the digital carrier range and can be a problem with the higher frequency SCAs. You can lower the quality or bit rate of the HD2 etc channels to help this situation a bit. It's a tradeoff, but the two systems can operate successfully together. RDS is a sort of SCA and it too runs just fine along with HD.

If the SCA injection level and/or deviation level is too high, that can cause problems with HD2 and higher, but if it's too low, some receivers may have a problem decoding it.

To clarify a bit: In standard (MP1) mode HD and HD2-3-4 channels use the same 96k data partition and won't interfere with SCA's or vice-versa - the carriers for the whole 96k partition are active no matter how many services you're using.

If you move into "extended hybrid" (MP3) mode, that adds a small partition closer in to the analog carrier. In this mode, you can encroach on the extended digital partitions if your baseband modulation exceeds 110%, though it doesn't have much of an effect on narrowband audio SCA's at 67kHz. I did try data at 67kHz with extended hybrid many years ago, and it didn't seem to affect anything, but it was far from a scientific test!

In MP3 mode the second partition is not added to the 96k primary partition - you're essentially getting another, separate 16k partition. You can put ancillary data in there, or throw in an additional audio channel (or two). Again though, it doesn't matter how much of that data is used - once the carriers are on, they're on. In theory if you exceed 110% analog baseband you could cause errors on that one 16k partition, but not the main, 96k one.

Doc in your opinion what would a typical SCA (or HD Sub Ch) lease cost on average for a metro area like Denver.

i have been trying to think of some legal backdoor ways of putting a FM signal on the air here in Denver without having to outright spend millions (which i don't have) on a existing station or new construction.

i was thinking of leasing an SCA or HD Sub and feeding a translator (or network of part 15 AM's) with it.

i have been trying to think of some unique programming idea's that are not heard around here. do something really community oriented with live DJ's.

the oldies and old time radio formats are already here.

maybe an outlet for alternative (unsigned artists) on FM.

my friend runs a neutral loaded carrier current am up in Casper, Wyoming covering about 4 miles over the power lines and the response to his alternative format has been great. if it can work in a small out of the way mid western town like there i bet it would go over great in a major metro area like Denver.

any way it has just been an idea on my mind for a number of years now.

kc8gpd

"The scientists of today think deeply instead of clearly. One must be sane to think clearly, but one can think deeply and be quite insane."

That's a tough one - it's one of those "whatever two people agree to" sorts of things.

Based on what some groups are paying in smaller markets, I'd say somewhere in the neighborhood of $2500-$4000/mo for an SCA lease in Denver on a full-market signal. HD sub channel would likely start around $5K in your area.

Of course, then you have to get SCA radios in the hands of the public in order to be heard. At that point, you're better off doing internet broadcasting - you'll have a bigger audience (same could probably be said for HD sub channels as well).

kc8gpd wrote:
i was thinking of leasing an SCA or HD Sub and feeding a translator (or network of part 15 AM's) with it.

Are you sure the FCC will let you carry a SCA on a translator? (nothing explicitly says you can run a HD sub either, but they obviously allow it. But I don't know of anyone carrying an SCA & would be careful about spending too much $$ without getting an answer.)

SCA on a translator is a non-starter. There is no provision for this anywhere in the Rules. HDx on a translator is the method of choice for some of the big broadcast groups to get around the ownership caps and hog available frequencies which would better serve the audiences you seek to reach, but that ship has sailed and is covered by a rather loose reading of the Rules which allowz a "main" broadcast audio program (which all HDx subchannels are considered) to be repeated on a translator. SCA is by definition not a "broadcast" signal.

Getting back to a comment above, the deviation (in KHz) of an FM carrier is not the same as the baseband bandwidth, which is why FM IBOC can coexist with analog subcarriers. As Doc mentioned, in some IBOC modes you have to watch the analog carrier deviation to keep the two out of each other but the subcarrier frequencies have little to do with that.

We are getting ready to stick HD on our big dog FM here. The possibility of HD and analog SCA interference is of real concern to me, as we have a tenant at 92 kHz.

If we stay with MP1 mode, from what I'm hearing there should be no impact on the 92 kHz subcarrier...but if we go extended hybrid, watch out. Since the object of the game is driving translators (sorry Deep), extended mode is a distinct possibility.

I have a question that maybe Doc or somebody else can answer. Are there minimum bandwidth requirements for the various HD streams? I seem to recall HD1 had to be at least 48 kbps, and the HD2-etc. were typically 16 kbps or higher, but is there a minimum for those?

There isn't a minimum for the secondary channels, though the audio isn't very good at all below 16k. I'd go ahead and try the extended mode with the subcarrier - as DT said, it's not really the location of the subcarrier that matters - deviation is deviation. The issue will be injection level. Your baseband will need to be under 110% with SCA's for extended hybrid and SCA's to behave.

Now, there is a loophole if you're feeding translators with HD sub channels. You are not required to actually feed the translator with the OTA HD signal - you can do a direct feed. However if your HD sub is off, the translator must be off as well. So, you could feed the HD sub at a lower bitrate and still feed the translator directly. That may preclude having to go to MP3 mode.

BroadcastDoc wrote:That's a tough one - it's one of those "whatever two people agree to" sorts of things.

Based on what some groups are paying in smaller markets, I'd say somewhere in the neighborhood of $2500-$4000/mo for an SCA lease in Denver on a full-market signal. HD sub channel would likely start around $5K in your area.

Of course, then you have to get SCA radios in the hands of the public in order to be heard. At that point, you're better off doing internet broadcasting - you'll have a bigger audience (same could probably be said for HD sub channels as well).

well that revelation just took the wind out of my sales for the idea.

i would need to get sponsorship ahead of time which i know is good luck on that.

guess i will just have to stick with my hobby radio.

kc8gpd

"The scientists of today think deeply instead of clearly. One must be sane to think clearly, but one can think deeply and be quite insane."

You might want to contact Hal Schardin, the CE for Minnesota State Services for the Blind. He's using FM Extra on Minnesota Public Radio stations all over Minnesota to transport Radio Talking Book. I know that he purchased a large number of receivers from someone for this project a few years back.